1. Field
The embodiment relates to a semiconductor device layout method and layout program concerning decoupling capacitances that are placed in a semiconductor device to prevent malfunction due to power supply noise.
2. Description of the Related Art
With the making of semiconductor devices finer and/or more highly integrated in recent years, operation power supply voltages are being made lower and/or operation frequencies are being made higher. However, when power supply noise is increased due to increase of the operation frequency on one hand while the operation power supply voltage is decreased on the other hand, malfunction and other adverse effects on circuit operations that accompany power supply noise become problematic.
As a countermeasure against such a problem, placement of decoupling capacitances for suppressing the power supply noise is considered. With a decoupling capacitance placement method disclosed in Japanese Unexamined Patent Publication No. 2006-40962, before placing logic cells, decoupling capacitances are placed in a target area in an averaged manner and then the logic cells are placed at areas free of the decoupling capacitances.
Upon partitioning the target area into a plurality of unit areas, an average consumption power is computed for each unit area from a total consumption power of the logic cells to be placed in the target area. The average consumption power is compared with the consumption power of the logic cells placed in each unit area, and whether or not the decoupling capacitance is inadequate is computed for each unit area.
If it is judged that the decoupling capacitance in a unit area is inadequate, a portion of the logic cells in the unit area is moved to another unit area or a logic change such that the consumption power of the logic cells in the unit area is reduced is made to make the decoupling capacitance adequate in the unit area.
Other related arts are disclosed in Japanese Unexamined Patent Publication No. 2004-55954 and Japanese Unexamined Patent Publication No. 2002-288253.